Magnetic tape remains economical for storing large amounts of data. For example, magnetic tape cartridges, or large spools of magnetic tape, are often used to back up data in large computing centers. Magnetic tape cartridges also find application in the backup of data stored on smaller computers such as desktop or notebook computers.
In magnetic tape, data is typically stored as magnetic signals that are magnetically recorded on the tape surface. The data is typically organized along “data tracks,” and transducer heads are positioned relative to the data tracks to write data to the tracks or read data from the tracks. Magnetic tape typically includes several data tracks in a data band. Other tape media, such as optical tape, holographic tape, and other tape media formats can also make use of data tracks. Tape media has the advantage of a very large surface area relative to disk-shaped media.
Servo patterns refer to signals or other recorded marks on the medium that are used for tracking purposes. In other words, servo patterns are recorded on the medium to provide reference points relative to data tracks. A servo controller interprets detected servo patterns and generates position error signals. The position error signals are used to adjust the lateral distance of the transducer head relative to the data tracks so that the transducer head is properly positioned along the data tracks for effective reading and/or writing of the data to the data tracks.
In a magnetic tape medium, servo patterns are often stored in specialized tracks on the medium, called “servo tracks.” Servo tracks serve as references for the servo controller. Servo tracks typically hold no data except for information that is useful to the servo controller to identify positioning of a transducer head relative to the surface of the medium. A plurality of servo tracks may be defined in a servo band. Some magnetic tape media include a plurality of servo bands, with data tracks being located between the servo bands.
Servo patterns are referred to as pre-recorded when they are recorded during the fabrication of the media. In other words, pre-recorded servo patterns are servo patterns recorded in the media prior to the media being used for storage of data. These pre-recorded servo patterns allow the media to achieve higher storage densities because the servo patterns enable positions on the media to be located with greater precision. Therefore, servo patterns allow for smaller amounts of media surface to be used to store units of data.
One example of pre-recorded servo patterns are amplitude-based servo patterns. For amplitude-based servo patterns, the detection of the servo signal amplitude enables identification of head positioning relative to the servo track. Another example of pre-recorded servo patterns are time-based servo patterns. For time-based servo patterns, the timing of the detection of successive servo marks enables identification of head positioning relative to the servo track. Other types of servo patterns also exist. Moreover, in some cases, servo patterns may be interspersed within data tracks.
Recently, a market for refurbished magnetic tape has emerged. Specifically, resellers may purchase or obtain used magnetic tape cartridges, repackage the tape cartridges, and sell the tape cartridges as refurbished media, typically at a discounted price relative to new tape cartridges. For magnetic tape that does not include servo patterns, the tape is typically degaussed in order to erase data content from the tape. For magnetic tape that includes servo patterns, however, degaussing is typically avoided. In this case, resellers typically use a drive to overwrite the data tracks in an effort to erase any data content prior to resale. Many companies claim that the used data storage cartridges are “recertified” in order to promote brand quality associated with the resale of such media.